1. Field of the Invention
The present invention relates to a structure of a steering arrangement applicable to an automotive vehicle and more particularly to an anti-vibration structure of the vehicular steering arrangement in which a dynamic damper is provided for damping a vibration of a steering wheel caused by a flexural vibration of a steering column regardless of a steering movement position and direction.
2. Description of the Prior Art
Conventional anti-vibration structures of the steering gear arrangements are exemplified by Japanese Utility Model Applications Unexamined Open No. Sho. 55-28,546 and No. Sho. 59-154,452.
The conventional anti-vibration structure disclosed in the former Japanese Utility Model Application has a feature that a dynamic damper having an inherent vibration frequency substantially matched with a resonance frequency point of the steering arrangement is installed within a post portion of a steering wheel attached to a tip of a steering shaft.
On the other hand, the other conventional anti-vibration structure disclosed in the latter Japanese Utility Model Application has a feature that the dynamic damper is housed within a space of a shaft housing comprising a pad mark fixed on a side wall of a supporting fixture fixed on an upper end of the steering shaft and a boss above which the pad mark surrounds, an attachment surface of an attachment bracket on which an elastic body constituting the dynamic damper is mounted vertically is in parallel to an axis center of the steering shaft, and the elastic body is arranged eccentrically with respect to the axis center of the steering shaft.
However, the above-described conventional anti-vibration structures of the steering arrangement have the following drawbacks.
That is to say, since in the structure of the steering arrangement disclosed in the former Japanese Utility Model Application the dynamic damper is installed on the post portion located on the axis end of the steering shaft, the post portion requires a large space at an upper part in the axial direction of the steering shaft so that the center of the steering shaft is largely projected toward a space of a driver's seat, thus the steering wheel being unsightly. In addition, since a relatively large space is created around the dynamic damper and base plate supporting the damper, an efficiency of utilizing space is reduced.
On the other hand, since in the other conventional structure of the steering arrangement in the latter Japanese Utility Model Application, the dynamic damper is installed eccentrically to the axial center of the steering shaft, the upper part of the steering shaft and accordingly a center part of the steering wheel is not largely projected toward the driver's seat and the spatial utilization efficiency is not reduced. However, since the axis direction of the elastic body constituting the dynamic damper is orthogonal to the axis direction of the steering shaft, the following problems arises.
The steering shaft usually generates a flexural vibration in the upper and lower directions thereof due to fluctuations of a vehicle body transmitted from a vehicular engine. Therefore, the steering wheel and dynamic damper both located on the upper end of the steering shaft also vibrate in the upper and lower directions. When the steering wheel is steered in an equibrium position so that the vehicle moves in the straight direction, the vibration of the steering shaft is inputted in a shearing direction of the elastic body so that the elastic body can produce a set spring constant and a mass body can resonate the vibration of the steering shaft in a specified way so as to damp the vibration. However, if the steering wheel is steered so that the vehicle moves in other directions than the straight direction, the vibration of the steering shaft acts on a compression direction of the elastic body so that the vibration direction of the steering shaft does not coincide with a displacement direction of an upper surface (facing toward the mass body) of the elastic body. Consequently, the spring constant of the elastic body varies, thus mass body connot be resonated so as to damp the vibration of the steering shaft.